Allison, Brian and Noah each have a 6-sided cube. All of the faces on Allison's cube have a 5. The faces on Brian's cube are numbered 1, 2, 3, 4, 5 and 6. Three of the faces on Noah's cube have a 2 and three of the faces have a 6. All three cubes are rolled. What is the probability that Allison's roll is greater than each of Brian's and Noah's? Express your answer as a common fraction.
Explanation: Since Allison will always roll a 5, we must calculate the probability that both Brian and Noah roll a 4 or lower. The probability of Brian rolling a 4 or lower is $\frac{4}{6} = \frac{2}{3}$ since Brian has a standard die. Noah, however, has a $\frac{3}{6} = \frac{1}{2}$ probability of rolling a 4 or lower, since the only way he can do so is by rolling one of his 3 sides that have a 2. So, the probability of both of these independent events occurring is $\frac{2}{3} \cdot \frac{1}{2} = \boxed{\frac{1}{3}}$.